Mold forming often in Walkin Refrigerator

Has anyone an idea of the reason Mold would be forming just about everywhere inside the cooler in just “TWO WEEKS” time in our 8 x 12 walk-in cooler? Having this same cooler since 2000 and the only change has been a new evaporator was installed a few years ago. Although that seems to be when it started forming quicker than before. Prior, It would take 6mos to a yr or more of a surface not cleaned to form mold on it. All penetrations are sealed up and door gaskets are not leaking. But it must have something to do with the humidity because its worse in the summer.

Yeah, it seems the humidity level in the walk in is higher than it used to be. The evaporator dehumidifies the air in addition to cooling it. Could your evaporator fan be running backwards? It should pull air across the coils towards the fan. The water that is removed drips to a pan that then drains out a tube. Is the pan tilted the wrong way and pooling before it finally drains? A partially clogged drain can also cause water to pool in the catch pan. Blow the tube out with compressed air to unclog it . This might cause higher humidity level. Is the tube leaking before it exits the walk in. Does the new evaporator run all the time or cycle on and off with the compressor?
Those are a few questions I’d ask about the evaporator.
A change of use can also cause issues. For example, are steaming hot liquids cooled in the walk in or first bench cooled?

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After more research, there are no malfunctions to equipment and the evaporator coil and the rooftop condenser are working as Their designed. We’re holding @ 40d because of produce in there and we retard our dough. The evaporator is always dry along with the drain pan.
The problem is it is not dehumidifying the air. We’re running 80% -90 % humidity. I just had my new Refrigeration company evaluate the equipment and they told me my 8x12 x7’ box calls for 8000 btu under normal use and 10000 btu under heavy use. The evaporator is rated for 9000 but but the rooftop condenser is rated at 12,900 btu. That’s the problem they think. Too much cold on the evaporator for too short of a time. Why would my old service company put a 12,900 compressor package on this system?

You could call the old refrigeration company to ask them. Maybe the length of the run to roof required a larger compressor?
When you say you hold at 40, does the temp controller bring the temp down to 34, turn off, then restart at 40? This is the range we always have used and the produce has done fine.

Hey, thanks for the follow up.
My new guy didn’t mention the line set length coming into play ( it’s only a 20-25’ run) and the old guy didn’t change it either even after my repeatedly questioning him pre and during the install. He sold the company right after my job so it’s over with him. The new company isn’t interested in having me as a client. ??
I don’t know the shutoff temp but yes there’s a range. The 24 hr high and low recently was 44-37. I’ll check that range again soon.

Just got the new quote to change the rooftop unit to a 9350 btu . $3500 plus $300 for a crane. Jeez.
My only other options are:
Limit moisture going into box
Set the box to a colder temp
Run a Dehumidifier in there 24/7
Add some artificial heat to make the box come on more often

I’d get a few more contractor opinions as to whether the compressor change will solve the mold problem.
Does the walk in have a digital thermostat or mechanical? I’ve replaced most of my mechanical thermostats with digital Rancho 111000’s as they are more accurate than the mechanical thermos I had. . Program it to turn on at 34, cut out at 40.
I assume your evaporator runs all the time(24/7). Yes?

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Great info. Ty
Yes, it’s the factory mechanical that came installed inside the enclosure on the Heatcraft Chandler Evap. I will inquire about that with my guy. a change out of compressor package should be my last alternative. FYI: my defrost timer was set for 60 min defrost every twelve hours, we have since changed it to 15 min every 4 hrs. I will also get a Better idea of my cut in and cut out temps and will certainly research that digital control you mentioned.